The overall aim of this research is to use aneurovirulent mutant forms of Herpes simplex virus (HSV) as direct gene transfer vectors to study the pathogenesis of Alzheimer's disease (AD). We will test the hypothesis that altered production or aberrant processing of amyloid precursor protein (APP) is directly responsible for the development of Alzheimer-like pathology in vivo. Genetically engineered recombinant HSV vectors will be used to introduce specific forms of the APP gene into the mature rat brain in a manner in which these genes are exclusively expressed from an otherwise quiescent viral genome during latency. We will also test a related hypothesis that chronic production of nerve growth factor (NGF) can rescue basal forebrain cholinergic neurons from age-related cell death using a similar vector. Finally, we will determine whether there exists an interrelationship between APP and NGF gene expression in brain using a combination of virus vectors. Three specific aims are outlined: (i) We will first complete development of HSV as a gene transfer latency vector for the rat CNS. The virus will be engineered to establish life-long latent infections in specific brain regions following direct stereotactic injection. Lac-z gene cassettes will be introduced into the virus vector at the U(s)3 locus using a Pl phage cre-lox recombination system and B-galactosidase expression from the latent HSV genomes will be induced in hippocampal cell populations using either the latency-specific (LAT) promoter or the neuron-specific neurofilament (NF) promoter. We will confirm that there is no virus -induced neuropathology created by the recombinant vector alone. (ii) The genes encoding for the full length APP, with and without the protease inhibitor insert, and the gene for the A4 fragment of APP, will be similarly recombined into the HSV latency vector and introduced into the hippocampus. We will determine whether any of these recombinants cause Alzheimer-like pathology in the rat brain, and whether these gene products effect the level of NGF expression. (iii) The gene for NGF will be expressed in hippocampus using an HSV::NGF recombinant latency vector in order to determine whether chronic NGF production can reverse the age-related loss of basal forebrain cholinergic neurons. We will also use expression from this vector in brain to determine whether chronic overproduction of NGF effects endogenous brain expression, and whether NGF delivered in this manner plays any role in modulating specific CNS pathology.___